Head Impact Telemetry System Research Articles

Baseline Neurocognition and Balance do not Influence Head Impact Severity in High School Football Players

Athletes with better neurocognitive and balance performance may have heightened field awareness allowing sufficient time to prepare for collision. Identifying football players who are at risk for sustaining high severity head impacts using baseline neurocognitive, balance, and symptom severity values could be a valuable concussion prevention strategy. PURPOSE: To compare head impact severity between football players with higher and lower baseline neurocognitive, balance, and symptoms. METHODS: Thirty-seven high school football players (height = 180.6±6.5 cm, mass = 87.3±18.6 kg, age = 16.6±0.9 years) completed a baseline evaluation including a computerized neurocognitive assessment (CNS Vital Signs), balance assessment (Balance Error Scoring System - BESS), and graded symptom checklist. Higher and lower performance groups were created using a median split for BESS total errors, total symptom scores, and the following neurocognitive measures: composite memory, psychomotor speed, reaction time, complex attention, cognitive flexibility, processing speed, executive function. The Head Impact Telemetry System was used to capture measures of severity for 16,066 head impacts (>10g): linear acceleration (g), rotational acceleration (rad/s2), and Head Impact Technology severity profile (HITsp - unitless). Random intercepts general linear models were used to compare head impact severity between higher and lower performers for each outcome measure (α = 0.05). RESULTS: Head impact severity did not differ between players with higher and lower neurocognitive and balance performance (p>0.05). Players reporting higher total symptom scores sustained higher linear acceleration (higher: 22.6g, 95%CI: 21.5, 23.7 vs. lower: 21.2g, 95%CI: 20.5, 21.9; F1,37= 5.10, p=0.030) and HITsp (higher: 14.2, 95%CI: 13.5, 14.9 vs. lower:13.3, 95%CI: 12.9, 13.8; F1,37= 4.24, p=0.046) compared to players reporting lower symptoms. CONCLUSION: Our results suggest that baseline neurocognitive and balance measures do not influence the risk of sustaining severe head impacts. Baseline symptoms may influence head impact severity, however, differences observed are not likely clinically meaningful. Researchers should continue to identify multidimensional factors associated with lessening concussion injury risk.

Comparing Head Impact Biomechanics between Professional, College, and High School Linemen

While head impact biomechanics studies have advanced our understanding of concussion, no studies to date have involved professional football players. PURPOSE: To examine differences in head impact biomechanics between 3 cohorts of offensive and defensive linemen: 1) National Football League (NFL), 2) College, and 3) High School (HS). METHODS: Players from 2 NFL teams (n=14; 6,127 total impacts), 1 college team (n=12; 7,138 total impacts), and 1 HS team (n=10; 4,136 total impacts) were enrolled in this study. The Head Impact Telemetry System (Riddell, Rosemont, IL) measured the following head impact variables: linear acceleration, rotational acceleration, and impact location. Data underwent a natural logarithmic transformation to normalize acceleration data prior to our analyses. We applied general linear mixed models to our acceleration variables and Chi Square tests to our head impact locations. RESULTS: We observed no significant differences for linear acceleration (F2,33=2.38, p=0.109) or rotational acceleration (F2,33=1.67, p=0.205) between cohorts. Analyses of the 95th percentile for linear acceleration and rotational acceleration revealed similar values for linear acceleration (NFL=62.2g, college=62.6g, HS=63.4g) and rotational acceleration (NFL=3859.9 rad/s2, college=3824.0 rad/s2, HS=4092.4 rad/s2) between cohorts. We observed an association between impact locations and the three cohorts (χ2(6)=676.58, p<0.001). The HS linemen experienced a significantly higher frequency of impacts to the front of the head (NFL=37.7%, college=34.3%, HS=53.4%) and a significantly lower frequency of impacts to the top of the head (NFL=19.4%, college=26.0%, HS=9.2%). CONCLUSION: Our head impact acceleration findings were expected given the literature has not identified any differences between HS and college cohorts to date. Future studies should explore speed and skill positions across competitive level. Many behavioral interventions are designed to educate HS football players on safe tackling techniques and the importance of ‘seeing what they hit.’ Our data show HS linemen experience more front-of-head and fewer top-of-head impacts. Future studies should measure the efficacy of these programs in light of the encouraging HS data we observed. Supported by the National Football League.

Abnormal white matter integrity related to head impact exposure in a season of high school varsity football.

The aim of this study was to determine whether the cumulative effects of head impacts from a season of high school football produce magnetic resonance imaging (MRI) measureable changes in the brain in the absence of clinically diagnosed concussion. Players from a local high school football team were instrumented with the Head Impact Telemetry System (HITS™) during all practices and games. All players received pre- and postseason MRI, including diffusion tensor imaging (DTI). Immediate Post-Concussion Assessment and Cognitive Testing (ImPACT) was also conducted. Total impacts and risk-weighted cumulative exposure (RWE), including linear (RWELinear), rotational (RWERotational), and combined components (RWECP), were computed from the sensor data. Fractional, linear, planar, and spherical anisotropies (FA, CL, CP, and CS, respectively), as well as mean diffusivity (MD), were used to determine total number of abnormal white matter voxels defined as 2 standard deviations above or below the group mean. Delta (post-preseason) ImPACT scores for each individual were computed and compared to the DTI measures using Spearman's rank correlation coefficient. None of the players analyzed experienced clinical concussion (N=24). Regression analysis revealed a statistically significant linear relationship between RWECP and FA. Secondary analyses demonstrated additional statistically significant linear associations between RWE (RWECP and RWELinear) and all DTI measures. There was also a strong correlation between DTI measures and change in Verbal Memory subscore of the ImPACT. We demonstrate that a single season of football can produce brain MRI changes in the absence of clinical concussion. Similar brain MRI changes have been previously associated with mild traumatic brain injury.

The Influence of Cervical Muscle Characteristics on Head Impact Biomechanics in Football

Background: An athlete is thought to reduce head acceleration after impact by contracting the cervical musculature, which increases the effective mass of the head. Purpose: To compare the odds of sustaining higher magnitude in-season head impacts between athletes with higher and lower preseason performance on cervical muscle characteristics. Study Design: Cohort study; Level of evidence, 2. Methods: Forty-nine high school and collegiate American football players completed a preseason cervical testing protocol that included measures of cervical isometric strength, muscle size, and response to cervical perturbation. Head impact biomechanics were captured for each player using the Head Impact Telemetry System. A median split was used to categorize players as either high or low performers for each of the following outcome measures: isometric strength (peak torque, rate of torque development), muscle size (cross-sectional area), and response to cervical perturbation (stiffness, angular displacement, muscle onset latency). The odds of sustaining moderate and severe head impacts were computed against the reference odds of sustaining mild head impacts across cervical characteristic categorizations. Results: Linemen with stronger lateral flexors and composite cervical strength had about 1.75 times’ increased odds of sustaining moderate linear head impacts rather than mild impacts compared with weaker linemen. Players who developed extensor torque more quickly had 2 times the increased odds of sustaining severe linear head impacts (odds ratio [OR], 2.10; 95% CI, 1.08-4.05) rather than mild head impacts. However, players with greater cervical stiffness had reduced odds of sustaining both moderate (OR, 0.77; 95% CI, 0.61-0.96) and severe (OR, 0.64; 95% CI, 0.46-0.89) head impacts compared with players with less cervical stiffness. Conclusion: The study findings showed that greater cervical stiffness and less angular displacement after perturbation reduced the odds of sustaining higher magnitude head impacts; however, the findings did not show that players with stronger and larger neck muscles mitigate head impact severity.

B-65 Thematic Poster - Hydration Assessment

Football players experience numerous blows to the head that may increase the risk for brain injury. While the majority of active football players are younger than high school age, investigations of head impact exposure (HIE) among youth players has been limited. Even less is known about the acute effects of HIE on neurological function in this population. PURPOSE: To measure HIE in youth football players over a full season and explore associations between HIE and changes in selected clinical measures of neurological function. METHODS: Twenty-two male middle school football players (11-14 yr) wore helmets outfitted with a Head Impact Telemetry System that uses six single-axis accelerometers to track and quantify head impact frequency, magnitude, duration and location. Impact data were collected for each practice and game during the season (27 practices, 9 games). Selected clinical measures of balance (BAL; AMTI force plate, NeuroCom Balance Master), oculomotor performance (OP; King-Devick Test), and simple reaction time (RT) were also assessed before (PRE) and after (POST) the season. RESULTS: The median number of head impacts per player was 252 (season), 80 (games) and 144 (practices), respectively. The maximum number of head impacts sustained by a single player was 880 for the entire season and 54 for a single session (practice). Approximately 48.8% of all head impacts had a linear acceleration between 10-20 g, 49.5% were between 21-80 g and 1.7% were greater than 80 g. Nearly all BAL, OP and RT measures were unchanged (P = 0.065 - 0.648 [BAL]; P = 0.079 - 0.221 [OP]; P = 0.346 [RT]) at POST. There were no POST deficits in any of the measures evaluated. CONCLUSIONS: This is the first study to examine associations between HIE and clinical measures of neurological function in middle school football players. Overall HIE in these players was found to be intermediate to what has been reported for younger and older (high school) players. Furthermore, these data suggest that the primary difference in HIE between middle school and high school football players is impact frequency. With no observed impairments in selected clinical measures of neurological function or a discernable relation between HIE and post-season deficits, an acute adverse effect of playing football on neurological function cannot be confirmed in this population.

B-44 Free Communication/Poster - Training Strategies and Performance

Athletes with stronger cervical musculature are thought to experience less severe head impacts. Strength is often quantified as the peak torque that a player can generate. A player is unlikely to activate the musculature maximally during the milliseconds over which a single head impact occurs. PURPOSE: To compare head impact severity between football players with stronger and weaker cervical musculature using both peak torque and torque-time variables. METHODS: Forty-nine high school and collegiate football players (height=183.12±7.31 cm, mass=94.02±21.35 kg, age=17.79±2.08 years) completed a pre-season isometric cervical strength assessment. Participants pushed their head against a padded strain gauge, reaching their maximum torque as quickly as possible, for three trials in flexion, extension, right and left lateral flexion. Players were separated into groups of stronger and weaker players using a median split for the following five composite (summed over all four directions) strength measures: peak torque (Nm*kg-1), rate of torque development (Nm*sec-1 – greatest slope within 50-ms sliding window), time to 50% of peak torque (ms), time to peak torque (ms), and torque impulse (Nm*sec). The Head Impact Telemetry (HIT) System was used to capture three measures of head impact severity during games and practices: peak linear acceleration (g), peak rotational acceleration (rad/sec2), and HIT severity profile (HITsp – unitless) (n=19,060 head impacts>10g). Fifteen random intercepts general linear models were used to compare head impact severity between stronger and weaker players (α = 0.05). RESULTS: We did not observe significant differences in head impact severity between stronger and weaker players for peak torque, rate of torque development, or time to half peak torque. Players who reached peak torque quickly sustained head impacts with higher HITsp values (15.02, 95% CI: 14.48, 15.58) than players who reached peak torque slowly (14.20, 95% CI: 13.75, 14.66) (F1,46=5.49,p=0.021). CONCLUSION: Overall, cervical muscle strength had little influence on head impact severity. In fact, players that reached peak strength quickly sustained head impacts of slightly higher severity. Cervical muscle strength may play a lesser role in mitigating head impact severity than originally thought.

Response

Dear Editor-in-Chief, Thank you for the opportunity to respond to the letter from Drs. Greenwald, Beckwith, Crisco, and Wilcox that raised concerns about the methodology and interpretation in our article (1). The authors highlight research in which the Head Impact Telemetry (HIT) System’s ability to detect impact has been corroborated through video review. These studies are designed to observe false positives—the HIT System reports a head impact that did not occur. However, these studies cannot identify false negatives—the HIT System does not report an impact that did occur. Like our study, which can and did detect false negatives, others (4) report a false-negative rate of approximately 20%. In the letter, the authors note that our article reported higher errors (lower coefficients of determination) than previously reported, but they incorrectly attribute this to limitations in our experimental protocol. The primary reason, however, is the difference in the error calculation method (see our Discussion, paragraph 3). We used a more conventional approach in statistical analyses (6) to estimate error associated with a given single measurement from the HIT System. Using this traditional definition of error with the data published in the most recent validation of the football HIT System in the letter of the authors (3), the error is 14% for linear acceleration, which is slightly lower than the error we reported (18%–31%) and greater than the 0.9% error reported in that article. In the letter, the authors raised concerns about the test biofidelity. The laboratory setting is generally a simplified analog of the real world, allowing for a systematic evaluation of test parameters on the outcomes of interest. We evaluated a range of impact directions and velocities, and we acknowledged (Discussion section, paragraphs 6–10) that other parameters such as fit, size, and material of the impacting surface likely influence the response. We elected to use the Hybrid III head form with limited structure on the underside of the chin and a spherical impacting ram for our testing to mimic published boxing (2) and football (3,5) studies by the authors. This, combined with the consistency of error results cited in the previous paragraph, suggests that our test protocol is as biofidelic as what has been used previously. Lastly, in the letter, the authors state that we “recommend applying [our] laboratory-derived ‘calibration factors’ to on-ice data without first considering plausibility.” We clearly stated in the Discussion (paragraph 4) that the published calibration factors “have potential,” but “further development of robust calibration equations should be subject of future study.” We commend the letter of the authors for developing the HIT technology and a business model that seeks to reduce the burden of TBI on society. We feel strongly, however, that the accuracy of such systems must be rigorously quantified as coaches and parents will make decisions about concussion risk and return to play based on player-specific data from such systems. We agree with the authors’ letter that validation is a multiphase process, and we recognize differences between in-play use and laboratory testing. Future research should incorporate laboratory-defined sensor accuracy into on-field investigations of injury risk and exposure. Kristy B. Arbogast, PhD Center for Injury Research and Prevention The Children’s Hospital of Philadelphia Department of Pediatrics, University of Pennsylvania Philadelphia, PA Mari A. Allison, BS Center for Injury Research and Prevention The Children’s Hospital of Philadelphia Department of Bioengineering University of Pennsylvania Philadelphia, PA Matthew R. Maltese, PhD Department of Anesthesiology and Critical Care Medicine, The Children’s Hospital of Philadelphia Philadelphia, PA John H. Bolte IV, PhD Yun Seok Kang, PhD Injury Biomechanics Research Laboratory The Ohio State University Columbus, OH

Limitations of “Validation Study of Helmet-Based Impact Measurement System in Hockey”

Dear Editor-in-Chief: Our team of researchers has extensively used Head Impact Telemetry (HIT) technology to investigate the relationship between head impact biomechanics and concussions. Members of our team invented and developed this technology specifically for these investigations, so we read with interest the recent article published by Allison et al. (1), describing a laboratory test that compared a hockey HIT System and a Hybrid III headform. Strong correlations were found between acceleration measurements; however, differences in peak accelerations were larger than those of other research-specific variants of the HIT System (2,5,7). In addition, a subset of trials was classified as invalid by HIT System data qualification algorithms. We believe the test protocol used in this study is inconsistent with on-ice use and led the authors to draw incorrect conclusions. The authors suggest that “…validation of the HIT System for ice hockey is extremely limited…” and a “comprehensive validation” is necessary due to “differences in accelerometer orientation, processing algorithm, and helmet shape.” To clarify, HIT System hockey helmets use the same accelerometer orientation, embedded electronics, and published (not “proprietary”) processing algorithms as previously validated boxing, soccer, and football research systems (2,4,5,7). In addition, on-ice performance has been corroborated through video review, and results have been consistent across multiple independent sites (3,6,8). The authors’ tests produced lower coefficients of determination and a more skewed relationship between acceleration measures than previous evaluations of similarly configured systems (2,5,7). We believe these discrepancies are primarily due to the substantial protocol limitations described by the authors. The hockey HIT System was designed for research and is not distributed commercially. To evaluate performance in the laboratory, helmet fit should be carefully controlled, as described in the literature (6), and test conditions (i.e., location, severity, and contact surface) should be representative of on-ice conditions and undergo verification for biofidelity (5,7). The authors described their helmet fit as a “worst-case scenario,” but it was actually unrealistic because there was no chin strap attachment and the facemask chin pad was disengaged from the headform. In addition, while 80% of on-ice impacts are attributed to contact with another player, including helmet-to-helmet, or flat surfaces (e.g., boards or ice) (8), this study delivered impacts using a noncompliant, spherical impacting ram, which is not a reasonable model of either condition. Interestingly, 19% of these tests were classified as uncharacteristic of on-ice impacts by the HIT System, demonstrating limited test fidelity and suggesting that a far more conservative interpretation of these results is warranted. Despite these substantial study limitations, the authors recommend applying their laboratory-derived “calibration factors” to on-ice data without first considering plausibility. If previously published, on-ice data from male hockey players (3) were adjusted by the proposed calibration factor, 5% of all impacts (15–20 impacts per player) would exceed 95g—a level typically associated with concussion. In addition, distributions of peak acceleration would be 58% (3) higher than in football, an unlikely outcome considering similar injury rates exist between sports. We agree that laboratory evaluations play an important role in assessing on-field measurement systems. Validation, however, should be a multiphase process that includes on-field/ice corroboration. The conclusions made in this study could lead to misapprehensions on hockey HIT System data, as well as misinterpretations of studies that have used this tool to advance the biomechanical understanding of concussions. Bethany J. Wilcox Brown University Providence, RI Jonathan G. Beckwith, MS Richard M. Greenwald, PhD Simbex Lebanon, NH Joseph J. Crisco, PhD Brown University Providence, RI

Validation of a Helmet-Based System to Measure Head Impact Biomechanics in Ice Hockey

This study aimed to quantify differences between head acceleration measured by a helmet-based accelerometer system for ice hockey and an anthropometric test device (ATD) to validate the system's use in measuring on-ice head impacts. A Hybrid III 50th percentile male ATD head and neck was fit with a helmet instrumented with the Head Impact Telemetry (HIT) System for hockey and impacted at various speeds and directions with different interfaces between the head and helmet. Error between the helmet-based and reference peak accelerations was quantified, and the influence of impact direction and helmet-head interface was evaluated. Regression equations were used to reduce error. System-reported impact direction was validated. Nineteen percent of impacts were removed from the data set by the HIT System processing algorithm and were not eligible for analysis. Errors in peak acceleration between the system and ATD varied from 18% to 31% and from 35% to 64% for linear and rotational acceleration, respectively, but were reduced via regression equations. The relationship between HIT System and reference acceleration varied by direction (P < 0.001) and head-helmet interface (P = 0.005). Errors in impact azimuth were approximately 4%, 10%, and 31% for side, back, and oblique back impacts, respectively. This is the first comprehensive evaluation of peak head acceleration measured by the HIT System for hockey. The HIT System processing algorithm removed 19% of the impacts from the data set, the correlation between HIT System and reference peak resultant acceleration was strong and varied by head surface and impact direction, and the system error was larger than reported for the 6-degree-of-freedom HIT System for football but could be reduced via calibration factors. These findings must be considered when interpreting on-ice data.

Estimation of Head Impact Exposure in High School Football

Background: Increased attention is being placed on the role of subconcussive impacts to the head during football participation and long-term cognitive health. Some have suggested that mitigating impacts to the head can be achieved by reducing or eliminating contact football practices. The effect that this might have on the number and magnitude of impacts is unknown. Purpose: To estimate the effect of limiting contact practices on the frequency and magnitude of head impacts through the retrospective assessment of in vivo head impact data. Study Design: Cross-sectional study; Level of evidence, 3. Methods: Data on impact magnitude and frequency were collected with the Head Impact Telemetry System during the 2009 football season among 42 varsity high school football athletes (mean age, 16.2 ± 0.6 years; mean height, 180.9 ± 7.2 cm; mean weight, 89.8 ± 20.1 kg). Head impacts were compared between player positions and session types (noncontact practice, contact practice, and game). These results were used to estimate the frequency and magnitude of head impacts when contact sessions were restricted. Results: The participants collectively sustained 32,510 impacts over the 15-week season. The typical athlete sustained a mean of 774 ± 502 impacts during the season, with linemen (center, guard, and offensive or defensive tackle positions) sustaining the highest number of impacts per athlete (1076 ± 541), followed by tight ends, running backs, and linebackers (779 ± 286); wide receivers, cornerbacks, and safeties (417 ± 266); and quarterbacks (356 ± 433). When viewed by session type, noncontact practices (n = 21) accounted for 1998 total impacts (2.4 ± 1.4 per athlete per session), contact practices (n = 36) accounted for 16,346 impacts (10.5 ± 7.7 per athlete per session), and games (n = 14) accounted for 14,166 impacts (24.1 ± 19.1 per athlete per session). Significantly more impacts occurred during games when compared with contact (P = .02) and noncontact practices (P < .001), and contact practices yielded significantly more impacts than noncontact practices (P = .02). Limiting contact practices to once per week would result in a 18% reduction in impacts for the duration of a season, while eliminating all contact practices would further reduce seasonal impacts by 39% across all players. Impact magnitudes were significantly highest during game sessions compared with contact and noncontact practices. Conclusion: Our findings suggest that limiting or eliminating contact football practices may reduce the number of head impacts sustained by athletes over the course of a season, although the effect that such rule changes may have on the magnitude of head impacts during practice sessions is less clear. As such, the potential effect of reductions in contact practices on athletes’ long-term cerebral health remains unknown.

On the accuracy of the Head Impact Telemetry (HIT) System used in football helmets

On-field measurement of head impacts has relied on the Head Impact Telemetry (HIT) System, which uses helmet mounted accelerometers to determine linear and angular head accelerations. HIT is used in youth and collegiate football to assess the frequency and severity of helmet impacts. This paper evaluates the accuracy of HIT for individual head impacts. Most HIT validations used a medium helmet on a Hybrid III head. However, the appropriate helmet is large based on the Hybrid III head circumference (58cm) and manufacturer's fitting instructions. An instrumented skull cap was used to measure the pressure between the head of football players (n=63) and their helmet. The average pressure with a large helmet on the Hybrid III was comparable to the average pressure from helmets used by players. A medium helmet on the Hybrid III produced average pressures greater than the 99th percentile volunteer pressure level. Linear impactor tests were conducted using a large and medium helmet on the Hybrid III. Testing was conducted by two independent laboratories. HIT data were compared to data from the Hybrid III equipped with a 3-2-2-2 accelerometer array. The absolute and root mean square error (RMSE) for HIT were computed for each impact (n=90). Fifty-five percent (n=49) had an absolute error greater than 15% while the RMSE was 59.1% for peak linear acceleration.

Subconcussive Head Impact Biomechanics

Recent literature suggests that subconcussive impacts may influence cognitive functioning across the life span. These effects are suggested to manifest as functional and possibly structural changes. Head impact biomechanics during American football have been characterized from the high school to professional level, but style of play has not been considered. The aim of this investigation was to quantify and compare head impact frequencies and magnitudes between two different offensive schemes. We investigated the frequencies and magnitudes (linear acceleration [g], rotational acceleration [rad·s], and HITsp) of head impacts sustained by 83 high school football athletes, playing for schools using two different offensive schemes. The two schemes comprised a run-first offense (42 athletes) and a pass-first offense (41 athletes). The Head Impact Telemetry System was used to record head impact measures. A total of 35,620 impacts were recorded across two seasons. Athletes in the run-first offense sustained an average of 456 head impacts per season (41 practices and 9 games), whereas the pass-first offense athletes sustained an average of 304 head impacts per season (44 practices and 9 games). The pass-first offense, however, sustained significantly higher impact magnitudes (P values < 0.05; 28.56g, 1777.58 rad·s, and 16.24) than the run-first offense (25.67g, 1675.36 rad·s, and 15.48) across a season. These data provide a first look at how different offensive strategies may influence head impact exposure in football athletes. In the study population, a run-first offense was associated with more frequent head impacts, of smaller magnitude, than a pass-first offense.

Isometric cervical muscle strength mitigates head impact severity

ObjectiveTo compare the risk of sustaining a mild, moderate, and severe head impact between athletes with high and low isometric cervical strength.DesignProspective cohort.SettingClinic/On-field.ParticipantsTwenty-one collegiate American football players.InterventionsIsometric strength was measured...

Brain injury prediction: assessing the combined probability of concussion using linear and rotational head acceleration.

Recent research has suggested possible long term effects due to repetitive concussions, highlighting the importance of developing methods to accurately quantify concussion risk. This study introduces a new injury metric, the combined probability of concussion, which computes the overall risk of concussion based on the peak linear and rotational accelerations experienced by the head during impact. The combined probability of concussion is unique in that it determines the likelihood of sustaining a concussion for a given impact, regardless of whether the injury would be reported or not. The risk curve was derived from data collected from instrumented football players (63,011 impacts including 37 concussions), which was adjusted to account for the underreporting of concussion. The predictive capability of this new metric is compared to that of single biomechanical parameters. The capabilities of these parameters to accurately predict concussion incidence were evaluated using two separate datasets: the Head Impact Telemetry System (HITS) data and National Football League (NFL) data collected from impact reconstructions using dummies (58 impacts including 25 concussions). Receiver operating characteristic curves were generated, and all parameters were significantly better at predicting injury than random guessing. The combined probability of concussion had the greatest area under the curve for all datasets. In the HITS dataset, the combined probability of concussion and linear acceleration were significantly better predictors of concussion than rotational acceleration alone, but not different from each other. In the NFL dataset, there were no significant differences between parameters. The combined probability of concussion is a valuable method to assess concussion risk in a laboratory setting for evaluating product safety.

Sports-Related Concussion Testing

Due to the recent focus on concussion in sports, a number of tests have been developed to diagnose and manage concussion. While each test measures different brain functions, no single test has been shown to quickly and reliably assess concussion in all cases. In addition, most of the current concussion tests have not been validated by scientific investigation. This review identifies the pros and cons of the most commonly used noninvasive tests for concussion in order to provide a more complete picture of the resources that are available for concussion testing. The potential utility of research tools such as the head impact telemetry system, advanced magnetic resonance imaging protocols, and biomarkers are discussed in the context of the currently employed tools.

Real-Time Head Acceleration Measurement in Girls’ Youth Soccer

The purpose of the current study was to collect real-time head acceleration data for soccer impacts during girls' youth (U14) soccer play. Linear and angular head accelerations were collected during girls' youth soccer scrimmages using a wireless head acceleration measurement device (the Head Impact Telemetry System). After field data collection, each individual impact was analyzed. The type of impact, header or nonheader, was determined, and nonheader impacts were further assessed by the category of impact. The head injury criterion and resultant linear and angular accelerations were analyzed and compared with current injury tolerance values for all impacts. A total of 47 header and 20 nonheader impacts were observed during the study. The front of the head experienced more headers than the other locations (n = 17). Header impacts ranged in peak linear acceleration from 4.5 g to 62.9 g and in peak angular head acceleration from 444.8 to 8869.1 rad·s(-2). The majority of the nonheader impacts (40%) were player collisions with other players. Only one goalpost collision occurred, but it resulted in the highest peak angular acceleration (5179.5 rad·s(-2)) and was the only nonheader impact to exceed any of the tolerance levels. Head accelerations were found to exceed the majority of previous laboratory studies. None of the impacts exceeded linear acceleration tolerance values for concussion, but angular accelerations did exceed the suggested limits. Three angular acceleration measurements for heading events (4509.8, 5298.3, and 8869.1 rad·s(-2)) exceeded the concussion tolerance values, but no concussions were diagnosed during the study.

Measuring Head Kinematics in Football: Correlation Between the Head Impact Telemetry System and Hybrid III Headform

Over the last decade, advances in technology have enabled researchers to evaluate concussion biomechanics through measurement of head impacts sustained during play using two primary methods: (1) laboratory reconstruction of open-field head contact, and (2) instrumented helmets. The purpose of this study was to correlate measures of head kinematics recorded by the Head Impact Telemetry (HIT) System (Simbex, NH) with those obtained from a Hybrid III (HIII) anthropometric headform under conditions that mimicked impacts occurring in the NFL. Linear regression analysis was performed to correlate peak linear acceleration, peak rotational acceleration, Gadd Severity Index (GSI), and Head Injury Criterion (HIC(15)) obtained from the instrumented helmet and HIII. The average absolute location error between instrumented helmet impact location and the direction of HIII head linear acceleration were also calculated. The HIT System overestimated Hybrid III peak linear acceleration by 0.9% and underestimated peak rotational acceleration by 6.1% for impact sites and velocities previously identified by the NFL as occurring during play. Acceleration measures for all impacts were correlated; however, linear was higher (r(2) = 0.903) than rotational (r(2) = 0.528) primarily due to lower HIT System rotational acceleration estimates at the frontal facemask test site. Severity measures GSI and HIC were also found to be correlated, albeit less than peak linear acceleration, with the overall difference between the two systems being less than 6.1% for either measure. Mean absolute impact location difference between systems was 31.2 ± 46.3° (approximately 0.038 ± 0.050 m), which was less than the diameter of the impactor surface in the test. In instances of severe helmet deflection (2.54-7.62 cm off the head), the instrumented helmet accurately measured impact location but overpredicted all severity metrics recorded by the HIII. Results from this study indicate that measurements from the two methods of study are correlated and provide a link that can be used to better interpret findings from future study using either technology.

Validation of Concussion Risk Curves for Collegiate Football Players Derived from HITS Data

For several years, Virginia Tech and other schools have measured the frequency and severity of head impacts sustained by collegiate American football players in real time using the Head Impact Telemetry (HIT) System of helmet-mounted accelerometers. In this study, data from 37,128 head impacts collected at Virginia Tech during games from 2006 to 2010 were analyzed. Peak head acceleration exceeded 100 g in 516 impacts, and the Head Injury Criterion (HIC) exceeded 200 in 468 impacts. Four instrumented players in the dataset sustained a concussion. These data were used to develop risk curves for concussion as a function of peak head acceleration and HIC. The validity of this biomechanical approach was assessed using epidemiological data on concussion incidence from other sources. Two specific aspects of concussion incidence were addressed: the variation by player position, and the frequency of repeat concussions. The HIT System data indicated that linemen sustained the highest overall number of head impacts, while skill positions sustained a higher number of more severe head impacts (peak acceleration > 100 g or HIC > 200). When weighted using injury risk curves, the HIT System data predicted a higher incidence of concussion in skill positions compared to linemen at rates that were in strong agreement with the epidemiological literature (Pearson's r = 0.72-0.87). The predicted rates of repeat concussions (21-39% over one season and 33-50% over five seasons) were somewhat higher than the ranges reported in the epidemiological literature. These analyses demonstrate that simple biomechanical parameters that can be measured by the HIT System possess a high level of power for predicting concussion.

High School and Collegiate Football Athlete Concussions: A Biomechanical Review

Researchers are striving to understand the biomechanics of concussive injury that occur in the context of sport by using a number of methodologies. Animal models, video reconstruction, and helmet-based accelerometers have all been used, but have their limitations. The Head Impact Telemetry (HIT) System permits the real-time in vivo tracking of all impacts that occur on the football field and has been used in both the high school and collegiate setting. This review provides a theoretical discussion of concussion mechanics and examines the current literature on the effects of the number of impacts, impact magnitude, impact distribution, and concussion threshold in high school and collegiate football athletes recorded by the HIT System.

The Relationship Between Subconcussive Impacts and Concussion History on Clinical Measures of Neurologic Function in Collegiate Football Players

Concussions sustained during college and professional football careers have been associated with both acute and chronic neurologic impairment. The contribution of subconcussive impacts to this impairment has not been adequately studied. Therefore, we investigated the relationship between subconcussive impacts and concussion history on clinical measures of neurologic function. Forty-six collegiate football players completed five clinical measures of neurologic function commonly employed in the evaluation of concussion before and after a single season. These tests included the Automated Neuropsychological Assessment Metrics, Sensory Organization Test, Standardized Assessment of Concussion, Balance Error Scoring System, and Graded Symptom Checklist. The Head Impact Telemetry (HIT) System recorded head impact data including the frequency, magnitude, and location of impacts. College football players sustain approximately 1,000 subconcussive impacts to the head over the course of a season, but for the most part, do not demonstrate any clinically meaningful changes from preseason to postseason on measures of neurologic function. Changes in performance were mostly independent of prior concussion history, and the total number, magnitude and location of sustained impacts over one season as observed R(2) values ranged between 0.30 and 0.35. Repetitive subconcussive head impacts over a single season do not appear to result in short-term neurologic impairment, but these relationships should be further investigated for a potential dose-response over a player's career.